The object of the present invention is the development of a process for the production of hydroxyl group containing .epsilon.-caprolactone modified acrylate or methacrylate resins cross-linkable with polyvalent isocyanates and the resinous products obtainable thereby.
There is already known from Fisk U.S. Pat. No. 4,082,816 a process for the production of .epsilon.-caprolactone modified acrylate and methacrylate resins. In this known process there is polymerized a mixture of 60 to 98 weight percent of at least one monomer of the group styrene, .alpha.-alkyl styrene and lower alkyl esters of acrylic and methacrylic acid and 40 to 2 weight percent of at least one hydroxyalkyl ester of acrylic or methacrylic acid together with .epsilon.-caprolactone in such an amount that 0.25 to 15 moles of .epsilon.-caprolactone correspond to one OH-equivalent of the monomer mixture, in the presence of a radical catalyst and a polymerization catalyst for the .epsilon.-caprolactone, advantageously in solution in a customary solvent. The entire disclosure of Fisk U.S. Pat. No. 4,082,816 is hereby incorporated by reference and relied upon.
If acrylate or methacrylate resins produced according to the known process are mixed with etherified melamine-formaldehyde resins and cross-linked on a deep drawable metal sheet by baking then the adhesion of the varnish coating to the base expressed as the grid cut value according to DIN 53151 (German Industrial Standard 53151) is very unsatisfactory. The adhesion of the varnish coating to the base is indeed somewhat better if in place of an etherified melamine-formaldehyde resin, there is used a known cross-linking agent for hydroxyl group containing methacrylate or acrylate resins based on polyvalent isocyanates, however, in many cases this is still insufficient.